The US is forming a "core coalition" to battle Islamic State militants in Iraq, senior American officials have said.

US Secretary of State John Kerry and Defense Secretary Chuck Hagel called for support as they held talks with officials from 10 nations on the sidelines of a Nato summiton a strategy to defeat IS.

"We need to attack them in ways that prevent them from taking over territory, to bolster the Iraqi security forces and others in the region who are prepared to take them on, without committing troops of our own," Mr Kerry said.

"Obviously I think that's a red line for everybody here: no boots on the ground," he added.

Mr Kerry said he was aware that many nations would not want to do military strikes, but he said they could provide intelligence, equipment or weapons.

The talks were held with defence and foreign ministers of Britain, France, Germany, Canada, Australia, Turkey, Italy, Poland and Denmark.

"This group here this morning is the core coalition," Mr Hagel told them.

IS controls large areas of northern Iraq and Syria

"It is the core group that will form the larger and extended coalition that's going to be required to deal with this challenge."

Speaking after the meeting, British Foreign Secretary Philip Hammond said: "The clear message coming out of here is that we have to have a comprehensive response to the ISIL challenge.

Video:'We Will Not Be Intimidated'

"It's not just about whether or not we should get involved in airstrikes. Everyone has a role to play and we should look at all elements, though it is clear we need regional support with a new and inclusive government of Iraq leading the efforts."

He reiterated that the UK had not made a decision on whether or not to take part in airstrikes.

The US has launched airstrikes in Iraq against the Sunni militants but is looking to expand its campaign after two videos showed the beheading of two American journalists held captive by the group, James Foley and Steven Sotloff.

IS - which is also known as ISIS and ISIL - has gained control over vast swathes of Iraq and Syria. It controls the territory with a strict interpretation of Islamic law and has gone after religious minorities.

The US stressed the need for a comprehensive approach to the crisis in talks on Friday and acknowledged that action against IS in Iraq would have implications in Syria as well.

"We're convinced in the days ahead we have the ability to destroy ISIL. It may take a year, it may take two years, it may take three years," Mr Kerry said.

"But we're determined."

Washington is looking to have solid plans in place by the time the United Nations General Assembly meets in two weeks.